Thanks for que quick answer JuanC.
There is not problem anymore, in fact I had not to change any code. The real problem was that as our test environment is a virtual server F5, temporary files were mixing an old version of the libraries with the new deployment ones. This caused inconsistencies, strangely only in IE.
It took me a little time to discover this because the development enviroment is in linux so we don't have IE to test, but your suggestion of a small sample was very helpful in finding what was happening.
Thanks again for you time.